Caribou are a large animal species found in the North American and Eurasian Arctic. The Porcupine Caribou Herd ranges in northwestern North America. The size of the Porcupine Caribou Herd depends on how many calves are
born and survive and how many adult animals die during the year. The herd reached a peak in 1989 at 178,000 and then declined until 2001 when numbers were estimated at 123,000 caribou. The last population estimate in 2013 was 197,000 caribou.*

The
Porcupine herd did not grow as quickly other North American herds during
the last decades of the 20th century. The birth rate during that period
was high and managers suspected that the Porcupine herd experienced
greater natural adult mortality than other barren ground caribou
herds. Biologists believed that the population decline in the 1990s was
probably related to weather conditions (high snow accumulations on the
wintering grounds and short summers in the early 90s). *

Porcupine Caribou parturition rate (percent of cows that had given birth or were judged to be pregnant). This information
is gathered from radio-collared caribou cows. Data Source: Alaska
Dept. of Fish and Game. From http://www.taiga.net/coop/indics/pchbirth.html. 2008